Severe gales, with gusts up to 120kmh in exposed places, were expected in Northland tomorrow morning, easing during the afternoon, and in Auckland about noon, easing at night.

Southwest gales could also become severe in exposed parts of the Coromandel Peninsula and western Bay of Plenty, MetService said

Widespread rain was expected as the low crossed the North Island.

The heaviest rain was likely tomorrow over eastern Bay of Plenty, Taranaki, Wairarapa, eastern Marlborough and the Kaikoura coast.

The deep low was expected to be about 150 kilometres west of Cape Reinga at midnight today and move rapidly southeast across the upper North Island tomorrow. It would be about 300km southeast of Hawke's Bay by midnight tomorrow.

Rain fell in parts of Northland, Auckland and Waikato this morning, brought by a warm front ahead of the former storm.

The front had "lots of moisture, bringing down humid, warm air full of rain", MetService meteorologist Liz Walsh said.

"It's going to be wet for a while."

MetService said there was a risk of one or two thunderstorms near the back edge of the rain band over the east of Northland to Great Barrier Island this afternoon.

Tonight, the risk was at Great Barrier Island, the Coromandel Peninsula and near the coast over the far east of the Bay of Plenty.

The rain will be welcome news for farmers in many areas of the North Island that have been drying out rapidly.

Much of Northland, Auckland, Waikato, the Central Plateau and the east coast of the lower North Island were as dry as they were at this time a year ago, when the country was heading into one of its worst droughts in a century.

The rain was expected to move south across the north of the North Island today, MetService said.